1. Field of the Invention
The present invention relates to a magnetic sensor element of a parallel flux gate type, small in size, and an electronic directional measuring device with the magnetic sensor elements mounted therein, and more particularly, to a magnetic sensor element of the flux gate type, small in size, and mountable in a portable terminal, and an electronic directional measuring device provided with three units of the magnetic sensor elements, arranged so as to be orthogonal in orientation to each other.
2. Description of the Related Art
An electronic directional measuring device has a feature in that a bearing can be electrically detected with the use of a magnetic sensor, and so forth. The electronic directional measuring device is generally made up by disposing a plurality of the magnetic sensor elements thereon. The magnetic sensor elements of the parallel flux gate type, like this, exhibit a linear output against a magnetic field parallel to an excited magnetic field. Accordingly, by performing computation on data obtained from respective outputs of the plurality of the magnetic sensor elements arranged so as to be orthogonal in orientation to each other, it is possible to calculate an angle from a direction decided as a reference, that is an azimuth. Because information on a bearing obtained from the azimuth can be processed in the form of an analog electric signal or a digital electric signal, hopes run high that the electronic directional measuring device will be applied to various electronic equipment, for example, a cellular phone, portable terminal such as PDA (Personal Digital Assistant), wristwatch, car-navigation device, a device for detection of an posture of an aircraft, a game player for use by the visually handicapped, and so forth.
Particularly, a service for providing position information, utilizing GPS (Global Positioning System), and so forth, intended for use by the portable terminal, has lately become available. With the service, a user can find out the present position information while watching a screen on the terminal. With the use of the terminal if combined with the electronic directional measuring device, the user can find out in which bearing he or she is oriented, or for which direction he or she is heading when walking. It is believed that an information service concerning the position information and the electronic directional measuring device will provide many sectors of the industry with an opportunity of new business in the future, offering useful information to the user as well.
Meanwhile, there has been seen a tendency of the portable terminal being rendered smaller in size as well as thickness, and an electronic device mounted therein is required to be small in size, and low in height. The magnetic sensor element as desired at present has a width on the order of several mm while a height thereof, 1.5 mm or less, is essential, and the height preferably 1.0 mm or less is in demand.
In order to solve such a problem as above-described, there has been proposed a magnetic sensor element of the parallel flux gate type, in a strip-like shape, that can be reduced in size (for example, refer to Patent Document 1).
Patent Document 1: JP 2004-184098 A (p. 6, FIG. 1)
Accordingly, an example of a conventional magnetic sensor element, disclosed in Patent Document 1, is described hereinafter with reference to FIGS. 24 to 26. FIG. 24 is a perspective view showing a makeup of the magnetic sensor element, FIG. 25 is a plan view showing a size of the magnetic sensor element, and FIG. 26 is a side view of the magnetic sensor element.
The magnetic sensor element 100 makes use of a permalloy film as a magnetic core layer 110, and is made up such that a coil 130 is wound round a middle part of a nonmagnetic base 120 with the magnetic core layer 110 stuck thereto, in the longitudinal direction thereof. Further, the magnetic sensor element comprises a middle part of the magnetic core layer 110, around which the coil 130 is wound, serving as a magnetism sensitive part 111, respective ends of the magnetic core layer 110, serving as magnetism collective part 112, and electrode pads 140 provided at respective ends of the nonmagnetic base 120. And by rendering the magnetism sensitive part 111 at the central part of the magnetic core layer 110, in the longitudinal direction thereof, smaller in cross-sectional area than the magnetism collective part 112 at respective ends of the magnetic core layer 110, magnetic fluxes are concentrated, thereby increasing a deviation amount on a B-H curve. If the magnetic sensor element is made up as above-described, dimensions thereof can be rendered on the order of 3 mm in length in the longitudinal direction thereof and 0.3 mm in width, as shown in FIG. 25, even if such properties described as above are imparted. The magnetism sensitive part 111 is formed to have a width on the order of 0.05 mm.
With a biaxial magnetic sensor (an electronic directional measuring device), wherein two units of the magnetic sensor elements are arranged in respective direction orthogonal to each other on the horizontal surface of a base, a height can be held to the order of 1 mm although a slight increase in width. Accordingly, it becomes possible to mount the electronic directional measuring device having the biaxial magnetic sensor in the portable terminal.
When the magnetic sensor element made up as described is rotated once in the same plane, the magnetic sensor element exhibits an output in a sinusoidal waveform. Two outputs of the biaxial magnetic sensor provided with two magnetic sensor elements disposed so as to cross each other at 90 degrees will be in a relationship whereby respective output waveforms are shifted in the phase each other by 90 degrees, and on the basis of the respective output, it is possible to calculate an azimuth. The magnetic sensor element of the parallel flux gate type capable of obtaining an output proportional to a magnetic field is based on following principle of detection.
First, a triangular wave current is applied to an excitation coil wound around the magnetic core layer. By the agency of a triangular wave magnetic field produced by the triangular wave current, the magnetic core layer repeats magnetization saturation and magnetization reversal along a B-H curve. As a pulse-like output is generated at the time of the magnetization reversal, the pulse-like output is detected by a detection coil. A pulse position will shift according to magnitude of an external magnetic field, if no change occurs to frequency of the triangular wave current. By taking out a change in time for pulse generation via a detection circuit, it is possible to obtain the output corresponding to the magnitude of the external magnetic field. In explanation given as above, the coils are described as separated between the excitation coil and the detection coil however, one coil can be used as both an excitation coil and a detection coil.
However, when a user attempts to obtain a direction with using a portable terminal provided with the electronic directional measuring device, which is the biaxial magnetic sensor having the function described as above, the portable terminal being in a tilted state (under a tilted environment), the following problem will occur to the electronic directional measuring device.
More specifically, it is presumed that the user of a portable terminal will adopt various use, and various manners of holding the portable terminal, and there can be the case where the magnetic sensor elements incorporated in the electronic directional measuring device are used in a tilted state against to a horizontal surface. Under such an environment as described, the biaxial magnetic sensor as described is incapable of calculating an accurate azimuth. For coping with the problem, three units of the magnetic sensor elements are prepared, and are disposed so as to be oriented along three axes orthogonal to each other, this will enable an azimuth to be accurately found even if the portable terminal is used in a tilted state against to a horizontal surface.
FIG. 27 shows an configuration example of an electronic directional measuring device made up by a triaxial magnetic sensor employing the magnetic sensor elements described in Patent Document 1 as previously described.
The conventional electronic directional measuring device as shown in FIG. 27, comprises an x-axis magnetic sensor element 100x, a y-axis magnetic sensor element 100y, and a z-axis magnetic sensor element 100z, disposed on the surface of the epoxy base 200, in such a way so as to be orthogonal to each other in the respective directions of the x, y, z axes. Further, the electronic directional measuring device comprises a magnetic sensor IC 300 for driving those magnetic sensor elements, and processing detection signals outputted from those magnetic sensor elements, respectively.
With a configuration described as above, there arises the need for disposing the z-axis magnetic sensor element 100z such that the longitudinal direction thereof is perpendicular to the x-axis magnetic sensor element 100x and the y-axis magnetic sensor element 100y, disposed along the horizontal two axes. Accordingly, a height of the electronic directional measuring device will become at least 3 mm or more (refer to FIG. 25). It is not possible to achieve a reduction in the height by mounting the electronic directional measuring device having the configuration described as above in the portable terminal, therefore that is not preferable.
Under the circumstances, in order to achieve further miniaturization of the conventional magnetic sensor element there occurs an idea of shortening the length of the element in the longitudinal direction. However, if the element is simply reduced in size, this will render it difficult to make effective magnetic fluxes to be converged. That is, with the magnetic sensor element in such a form, the effect of a demagnetizing field, due to a geometric effect, will become remarkable, so that magnetic fluxes collected at the respective magnetism collective part 112 shown FIG. 24 will no longer be effectively converged onto the magnetism sensitive part 111.
Further, if widths of the respective ends of the magnetic core layer 110 (widths of the respective magnetism collective part 112) are rendered larger in comparison with a width of the central part thereof (a width of the magnetism sensitive part 111) in order to make external magnetic fluxes to be effectively collected by the magnetic sensor element 100 shown in FIG. 24, this will cause a width of the nonmagnetic base 120 as well to be rendered accordingly larger. Then, an excitation current necessary for causing the magnetism sensitive part 111 to undergo magnetization saturation will become considerably large in magnitude, thereby rendering it practically difficult to cause occurrence of the magnetization saturation.
Further, as another means for reducing the size of the magnetic sensor element in the longitudinal direction, there occurs another idea of keeping the coil in intimate contact with the magnetic core layer and winding the coil around thereof, thereby reducing the central part of the nonmagnetic base 120 as well as the magnetic core layer 110 into a constricted shape. However, it is extremely difficult to reduce the nonmagnetic base 120 into the constricted shape or the like by applying micromachining thereto. Even if the nonmagnetic base 120 can be formed in the constricted shape, the coil will become prone to be very easily broken when the coil is wound around because the width of the central part (the width of the magnetism sensitive part 111) has to be rendered 0.1 mm or less.
Accordingly, with the conventional magnetic sensor element as shown in FIGS. 24 to 27, it is appropriate to render the width of the element on the order of 0.3 mm, and if the width of the element is rendered smaller than that, this will render it difficult to detect geomagnetism, which is not preferable in making up an electronic directional measuring device.